var maxMove:Number =50;

var bounds:Rectangle = new Rectangle(this.volumeSlider.x, this.volumeSlider.y, -maxMove, 0);
var scrolling:Boolean = false;
 
function startScroll (e:Event):void {
   scrolling = true;
   this.volumeSlider.startDrag (false,bounds);
}
 
function stopScroll (e:Event):void {
   scrolling = false;
   this.volumeSlider.stopDrag ();
}
 
function enterHandler (e:Event):void {
   if (scrolling == true) {
      MovieClip(this.root).setVolume(1-((bounds.x-this.volumeSlider.x)/maxMove));
   }
}

function setVolume(vol:Number){
   var mod:SoundTransform = new SoundTransform();
   mod.volume = vol;
   mp3Channel.soundTransform = mod; //apply to yout mp3Channel
}

addEventListener (Event.ENTER_FRAME, enterHandler);

this.volumeSlider.addEventListener (MouseEvent.MOUSE_DOWN, startScroll);
stage.addEventListener (MouseEvent.MOUSE_UP, stopScroll);

http://www.project13.pl

Simple yet effective way to create a horizontal slider to controll the volume of your sound channel

AS3 Volume Slider

script, flash, 3

ActionScript 3